1. Field of the Invention
The present invention relates in general to an electro-mechanical transduction apparatus. More particularly, the present invention pertains to an electro-mechanical spring apparatus that is based upon flextensional transducer techniques. Even more particularly the present invention relates to an acoustic transduction device which in particular is adapted to provide large displacement at low resonant frequencies.
2. Background Discussion
Underwater acoustic transducers typically utilize piezoelectric or magnetostrictive materials to produce intense acoustic signals. Since these materials are quite stiff, the design of a compact piston transducer which resonates at low frequencies becomes difficult to achieve unless, of course, a large mass is used. This is not always a satisfactory solution as it increases the energy stored and raises the mechanical Q of the system. Accordingly, systems with lower stiffness, such as an electrodynamic or a variable reluctance mechanism are often used as low frequency resonators. These systems, however, are generally not sufficiently rugged, particularly in connection with the environmental conditions imposed upon such transducers.
One solution for the stiffer drive systems, such as systems using piezoelectric ceramic material, has been to use flexural bars or plates driven into a low frequency bending mode by means of piezoelectric material attached firmly to one side or both sides of the plate. Multiple units may be connected together in mechanical series to increase the displacement and obtain a low resonant frequency. A difficulty with the bending plate is that the piezoelectric material is directly attached to the bending plate and this construction limits the amount of stress in the vibrating system since the ceramic material is quite weak in tension. Also large stresses can effect the electro-mechanical performance.
Reference is also made to the field of flextensional transducers. In a flextensional transducer only the shell (typically a metal) bends and radiates energy. The flextensional transducer patents of H. C. Hayes, U.S. Pat. No. 2,064,911 (Dec. 22, 1936), W. J. Toulis, U.S. Pat. No. 3,277,433 (Oct. 4, 1966) and H. C. Merchant U.S. Pat. No. 3,258,738 (June 28, 1966) show means for obtaining low frequency resonances with the use of magnetostrictive or piezoelectric active material as a driver along the major axis of a shell in the form of an ellipse or oval shape. These devices, however, normally radiate from both sides and baffles are generally needed to control the radiation. Also, the vibrating surface does not vibrate with a uniform velocity and most of the radiating surface moves with a velocity less than the peak value at the center line of the shell.
Accordingly, it is an object of the present invention to provide an improved electro-mechanical transduction apparatus.
Another object of the present invention is to provide a compliant electro-mechanical spring transduction device in which either piezoelectric or magnetostrictive members provide motion that is magnified by a flextural-extensional (flextensional) induced bending motion for providing large displacements.
A further object of the present invention is to provide an improved electro-mechanical transduction apparatus that provides a low frequency large displacement, and embodied as a piston transducer in relatively compact construction.
Still another object of the present invention is to provide an improved electro-mechanical spring that is energized by piezoelectric or magnetostrictive material and in which the spring amplifies the motion of the active material and is combinable either in series to obtain greater displacement or in parallel to obtain greater force.
Another object of the present invention is to provide an improved electro-mechanical transduction apparatus that may be embodied either as a spring, valve or actuator.